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Why are propeller engines uncommon on airliners?
My experience in aviation is essentially zero, but looking at Wikipedia it seems like the Tu-95 Bear offers high subsonic speed and extreme range.
I assume that turboprop engines are more fuel efficient than jet engines. If all the above are true then why we do not get to see more rotary engine planes in commercial airline flights?
Is it a noise concern? I see that the TU-95 is apparently the "noisiest military aircraft on Earth".

There are different ways to make thrust, which is a force, equal to mass x acceleration.  Turbojets take a relatively small mass of air and accelerate the heck out of it (acceleration = noise).  A turbofan grabs a larger mass of air and accelerates it less.  A turboprop grabs an even larger mass of air and accelerates it less.  A helicopter's rotor grabs a tremendous mass of air and accelerates it relatively little.  The engines on a 747 and the F-16 produce approximately the same amount of thrust, but the 747 (high-bypass) burns less fuel/hour and the F-16 (low bypass) has a higher top speed.

Well, first let's clear up a few terms:
When you say "rotary" engine I'm assuming you're referring to radial engines, a type of piston engine that used to be pretty common on aircraft. (These days opposed piston engines are what you typically find on piston-powered aircraft, rotary engines are yet another design, but their usage died out around the end of World War I.)

The TU-95 is not actually a piston-powered aircraft.  It's a turboprop – basically a turbine engine similar to what you'd find in a jet, only rigged up to turn a propeller rather than produce "jet thrust" directly.
From an efficiency standpoint, turbine engines are usually more fuel efficient than their piston counterparts, and jet fuel is denser and less refined than aviation gasoline and is consequently cheaper for operators to procure. Turbine engines also offer more reliability than piston engines, and the maintenance on a turboprop engine is also largely similar to a jet engine with a few extra components, which is an advantage for a company operating a fleet of jet and propeller driven aircraft.
The differences in operating efficiency and reliability are the major reason why gasoline-powered piston engines have basically disappeared from scheduled airline service.

So why don't we see more turboprops? Actually we see a lot of them, if you look in the right places.
Jets and Turboprops are good at different things: broadly simplifying, a turboprop is more efficient at lower altitudes and airspeeds while a jet engine is more efficient at higher altitudes and airspeeds.
As a result we see turboprop aircraft like ATR 72s in use for short-haul "commuter" service, but for trans-continental or trans-oceanic flights where they spend a long time cruising at high altitude jets dominate the sky.
Since most people are flying to go relatively long distances there are comparatively more jets in scheduled airline service than turboprops.
Noise is probably also a factor: fast turboprops like the Bear are LOUD not due to the engine, but due to the propeller.  The tips of the spinning propeller on a TU-95 can approach supersonic speeds, which causes quite a bit of noise. The TU-95's contra-rotating propellers (which help produce thrust more efficiently) also contribute to a louder noise footprint.  In the case of the TU-95 this doesn't matter – it's a military plane, and the Russian air force doesn't care if people complain as the aircraft has a mission to complete and that's more important than a few noise complaints.  If United Airlines were to operate a TU-95 out of Kennedy departing over people's houses I suspect they would quickly reconsider their choice of equipment when the noise complaints started coming in....

I would also add that a lot of turboprops have been replaced by regional jets because of public misconceptions that jets are safer, so we see them a lot less often than we used to.

Well mechanically speaking there is a lot less to break in a jet than a turboprop, and less in a turboprop than a piston engine :-)

Well, turboprops have a lot of advantages over jets too (not the least of which is that they generally fly slower/use less runway), but it isn't as comfortable for passengers, and they get stuck lower (in more weather, turbulence, etc.) and people don't like that.

when i mentioned rotary engine , i meant planes with propellers :D Thank you for this complete explanation

@Lnafziger,people are willing to trade convenience for cheaper fares, as can be seen from cheap airliners like easy jet.

Actually it seems turboprops are less fuel-efficient than pistons (especially then diesels, which can additionally also burn Jet-A). They are however lighter, simpler and more reliable.

@JanHudec - that depends on your metric. A piston engine is more efficient in terms of gallons per hour or miles per gallon, but in terms of passenger-miles a turboprop is more efficient simply because the extra power allows the engine to haul a bigger aircraft along with it.

@JonStory: No, I am thinking about joules per kilogram (BSFC (ok, that's inverse, kilograms per joule, does not really matter)), which means I am comparing engines of equal shaft power capable of hauling aircraft of the same size only. Comparing engines with different power would be obviously silly.

Another possible definition of a rotary engine is a Wankel.

when i read the question, i thought he was talking about these rotary engines.

@Lnafziger - There is one situation in which turboprops in nacelle mounts on the wings are significantly less safe than a turbofan in the same configuration; blade-outs. If a propeller blade becomes separated from the propeller hub at just the wrong time, its momentum can put it all the way through the plane's fuselage. Example: http://aviation-safety.net/database/record.php?id=19690803-1 Modern turbofan engine housings are designed specifically to contain a broken blade.

about the noise: https://www.youtube.com/watch?v=q-2dfEc70gU

@JanHudec is correct. Diesel piston engines beat turboshafts because of their higher compression ratio, even comparing at cruise. However, I personally find it more intuitive to think of it in terms of supplied torque (Newton-meters) per fuel consumption rate (kg/s), which comes out to square meters per second just like Joules/kg does. Unfortunately this is only good for piston props and turbo props, and is not good for any kind of jet. That would require thrust per fuel consumption (N/(kg/s)) = m/s, which requires we also get the prop engine's thrust instead of just power.

@KeithS: On the other hand, if a full rotor disk blows on a turbofan, not even the engine cowling can stop it, and it can potentially do damage far worse than what is possible from even the entire propeller coming apart on a turboprop.

As for the Tu-95 being a military rather than a civilian aircraft, there actually was a passenger variant thereof - the Tu-114.  Never formed part of United's fleet, though, and I don't know if it ever operated into/out of JFK.

Downvote for the false statement "turbine engines are usually more fuel efficient than their piston counterparts"

Reading the answers here tells me to put a few facts into the discussion:

Piston engines are the most fuel efficient aviation engines. Their drawback is a constant power output over speed, so that thrust is inverse to speed. This helps for acceleration at take-off, but limits maximum speed. A modern piston engine uses 240 g of fuel for providing 1 kW of power over one hour: 240 g/kW-h. Diesel engines use as little as 220 g/kW-h. This number is already true for the old Jumo 205, among the first aviation diesel engines in operation 80 years ago.
Turboprop engines are next, and their power increases a little over speed due to ram pressure (which will raise the internal pressure in the engine by approx. 30% at Mach 0.8). Their power-specific consumption is about 300 g/kW-h.
Jet engines are less efficient than both, but are better for flying fast and high. Their thrust drops even less with speed, so the better basis for expressing consumption is thrust, not power. The typical fuel consumption of a modern jet engine (GE-90) is 30 grams of fuel per Newton of thrust over one hour (30 g/N-h) when run stationary, and twice that in cruise at Mach 0.8. Modern Military jet engines achieve 80 g/N-h at take-off and have roughly constant thrust and specific consumption over speed.

In all cases, thrust is created by accelerating a mass of air backwards. The general equation for propulsive efficiency $\eta$ is $$\eta = \frac{v_{\infty}}{v_{\infty}+\frac{\Delta v}{2}},$$ where $\Delta v$ is the speed increase of the mass of air due to that acceleration. This formula shows that it is better to accelerate a big mass of air only a little than a smaller mass by a lot. Propellers do this and for that reason offer the best efficiency. Turboprops use less efficient, but lighter gas turbines for creating power, but retain the efficient propeller. Civilian turbofans try to increase the mass of air by increasing their bypass ratio, and only the military is using the least efficient types with bypass ratios below 1, because they are the best choice at supersonic speed.
Below you see a plot of the thrust-specific fuel consumption in cruise condition of different engine types over their bypass ratio. The inverse relation is easily visible.

Plot of the thrust specific fuel consumption in lb of fuel per lb of thrust per hour of different engines over the logarithm of their bypass ratio (picture source).
To make a comparison between piston and turbofan engines possible, let's compare fuel consumption at take-off. The formula for static thrust of a propeller is
$$T_0 = \sqrt[\Large{3}\;]{P^2\cdot\eta_{Prop}^2\cdot\pi\cdot d_P^2\cdot\rho},$$ where $P$ is the shaft power, $d_p$ the propeller diameter and $\rho$ the air density. For our example, we use a four-bladed prop of 3.4 m diameter and an engine with 1111 kW power. Its static thrust is 10.727 kN when we assume standard atmospheric conditions and a prop efficiency of 85%. The fuel flow will be 266.6 kg per hour, and relative to thrust this is 24.8 g/N-h or just 80% of that of a modern turbofan.
I wonder if even the enthusiasts could guess what airplane I used, because I obfuscated it by using those unfamiliar metric units. I guess nobody will argue that it is not optimized for fast flight, so this comparison should also hold for the Tu-95, for which I have less data available.
However, a propeller will force any aircraft to fly more slowly than jets. Their efficiency tanks once the propeller tips rotate at supersonic speed, so it is best to keep cruise Mach below 0.6. But commercial traffic wants to fly as fast as economically possible, and with turbofans this limit is only reached around Mach 0.85. The faster aircraft will fly more legs in the same time, carrying more people and earning more revenue. Also, by offering the faster connection, it will turn up in the booking systems on page 1 and be the favorite with business travelers, who account for almost all the profits of airlines. That is why we do not see many turboprops in civilian traffic anymore.

Just curious, why are you using a symbol like $v_\infty$ instead of something like $v_0$ or $v_i$? Where does infinity come into it? Also I want to point out that piston engines and turboprops use different fuels, so someone may be curious to multiply these efficiencies by their specific energy (MJ/kg) to see if it makes any difference. As it turns out, Avgas specific energy is about 43.5 MJ/kg and jet-A1 is 43.15, so it makes very little difference.

@DrZ214 The infinity should signal that this air speed is for undisturbed air which has not been influenced by the pressure field of the aircraft or the propeller. Theoretically, only at infinity is this condition true.

Nice answer bui you implies efficience is trust/weight of fuel. Since turbojets and faster how it compares when you mesure mile/weight of fuel?

@jean: The speed difference is not so big that it will make a difference. Propeller engines are still more efficient, even on a gallon per mile basis. Of course, you need to compare the same technology standard to come to this conclusion.

Another drawback of piston engines: their terrible reliability.

Noise should not be the problem. Modern turbo prop driven aircraft are even more quiet compared to similar aircraft driven by jet engines. It is - like always - all about economy.
Let's talk about the available engine types. (All you experienced aviators, I'll keep it very simple and so in some points even not 100% correct. If you don't like this, please skip this paragraph, if you like to have moe details on an engine type, please feel free to ask your questions) Piston engines are the earliest engines and still most common or light sport aircraft. You can compare them to the engine in your car, but instead of driving the gearbox which drives your wheels, they drive a propeller (sometimes also via a gearbox). Piston engines strong enough to power an airliner, as they did in the past, consume far too much fuel and oil to be efficient enough to compete with jet engines.  There are different types of jet engines. The classic jet engine sucks in air with its fan, squeeze it in a compressor, makes it go bang in a combustion chamber and blows it out, while a turbine ahead of the nozzle uses a bit of this energy to drive the fan and the compressor - remember this four words and you will always know how it works ;) This simple kind of jet engine was used for early jet driven passenger planes, but nowadays you'll only find it in military jets. Modern passenger aircraft use the same principle, but their engines have a far bigger fan turbo fan engines. Most of the air is bypassed around the "core" of the engine. This air delivers more than half of the thrust.. There are also turbo prop engines: simply replace the fan with a propeller. And finally turbo shaft engines where all of the jet engines power is used to drive a propeller and the exhaust delivers no forward energy.
Where does all this noise come from? To keep it simple, we can say that differences in speed produce noise. Jet engines are noisy because of the high difference in speed of the air passed through the engine and the free air stream. The cold air stream of a turbo fan engine is slower so there is less speed difference at the exhaust and less noise. The noise of propeller engines is mostly dependent on the speed of the propeller. The tips of the propeller blades are obviously the fastes moving parts. Their design requires them to remain subsonic to deliver thrust but propeller speed as well as the speed of the fan in turbo fan engines is more and more reduced to reduce noise emissions.
An economic engine must not only be quite but also powerful as well as fuel efficient. You are right turbo prop engines are generally the most fuel efficient engines but would you as a passenger like to sit ten hours in an airplane to get from London to New York? I don't and most airliners won't like such a plane too, because flight time costs money. Turboprop aircraft are most efficient on short distances where the difference in speed doesn't makes such a huge difference in flight time.
Another problem with turbo prop engines are the passengers. There are many people who see an propeller and think that they are sitting in one of the oldest airplanes ever. They trust in jet engines,  low wing design and everything you would find on an "modern" passenger airplane drawn by a seven years old child.
I hope you'll find your answer, considering all this really basic and simplified knowledge.

You mention "urbo prop engines are generally the most fuel efficient engines but would you as a passenger like to sit ten hours in an airplane to get from Londn to New York?" , i mentioned Tu-95 because of same speed as an airliner

Okay, have a guess what it needs to accelerate and maintain an aircraft like this at this speed in straight and level flight. You need a lot of power. Those NK-12 engines are able to deliver this ammount of power but i terms of fuel efficiency they are not comparable to modern jet engines. It might be possible, that we will see more propeller driven aircraft in future, even on longer routes, but these aircraft aren't developed yet. Also some kind of hybrids between turbo fan and propeller in the free air stream are under consideration. Refer to this link: http://en.wikipedia.org/wiki/Propfan

Interestingly, in the late 1980s GE worked on a high-efficiency design known as an unducted-fan (UDF). It was based on an existing turbofan core but had a series of short, curved blades that were mounted on a ring that formed the outer perimeter of the engine. In essence, the fan was on the exterior of the engine. They achieved about a 30% reduction in fuel consumption, but suffered from noise issues. Boeing was interested in using these engines on a new narrow-body aircraft design (7J7) to replace the 737. Lower fuel prices and high development costs led to the cancellation of the projects.


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How do I tell a Garmin 430 not to exit a hold?

Let's say that we're directly west of CATLI and have been cleared direct CATLI for the RNAV approach.  We load the approach into the GNS430 and proceed direct the fix.
After crossing CATLI outbound for the hold-in-lieu-of-procedure-turn, we realize that we want to stay in the hold for a few more turns.  How do I tell the 430 that I don't want it to sequence to ZAMGI upon arrival at CATLI?

Press the OBS button to put waypoint sequencing into suspend, as indicated by the green "SUSP" appearing over the OBS button.

Knew it was something simple.

Yep. The OBS button acts as suspend button:
-in holds
-on the leg between FAF and MAP
-if on the "from" side of the leg to the IAF, if vectors-to-final is activated.

source: Stack Exchange

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What makes the swooping noise when a jet flies overhead?
I've lived near several airports and have grown accustomed to a certain noise a jet plane makes when passing overhead: a swooping sound, very bass-heavy, that dives rapidly in pitch, maybe 1.5 seconds in duration. It happens toward the very beginning of the plane's audibility and is followed by the normal sound of the jet passing above.
Is it simply the Doppler effect as the plane passes overhead and its noise rapidly changes?
Or is there a mechanism on the airframe whose actuation on an approach might make this sound? Sometimes the same plane makes this sound more than once, which makes me think it isn't simply the Doppler effect.

The Doppler effect - partly covered by some of the answers here: http://aviation.stackexchange.com/questions/14557/how-does-altitude-affect-sound

Could be a chang in engine speed as well.  If power is increased or reduced you will hear a relatively loud "spooling" noise.

Interestingly gliders make an almost identical sound when they fly overhead, they sound just like jets, so it's not just the engine noise. Good to listen when they're 100ft above you.

The effect you noticed is the result of the combination of Doppler effect and sound absorption.
Sound absorption in a fluid is proportional to
$exp(- \alpha \nu^2 x)$
where $\alpha$ is a dimensional constant, $x$ is the traveled path, and $\nu$ is the sound frequency.
In its own reference frame, the airplane emits always the same sound, irrespective of whether it is approaching or receding from the observer. But for the observer, the frequency of a wave (which is $\nu_0$ in the plane frame) seems $\nu_a = \frac{\nu_0}{(1-v_j/c_s)}$ when the airplane is approaching, and $\nu_r = \frac{\nu_0}{(1+v_j/c_s)}$ when the plane is receding (here $c_s$ is the sound speed and $v_j$ the airplane's speed). Thus the perceived frequency jumps by a factor
$F = \left(\frac{1+v_j/c_s}{1-v_j/c_s} \right)$
This means that the absorption coefficient, at the time when the airplane is passing overhead (thus $x \approx H$, the plane's height over the ground), jumps from
$D_a = \exp \left(\frac{-\alpha H \nu_0^2 }{(1-v_j/c_s)^2}\right)$
to
$D_r = \exp\left(\frac{-\alpha H \nu_0^2 }{(1+v_j/c_s)^2}\right)$
For typical values for the atmosphere, and the propagation of sound waves in it, this means that $D_a \ll 1$, while $D_r \approx 1$.
Hence, what is happening is that, as the airplane passes roughly overhead, the sound goes from being deeply absorbed, especially at high frequencies, to not being absorbed at all (its normal sound, as you call it). The strange sound you noticed is what you perceive as the lower frequencies are becoming less and less absorbed, and thus the sound spectrum changes.
EDIT 1:
after I wrote my reply, DClayton (in a comment above) gave a very important hint that this is exactly what is happening when he noticed that the same effect appears with gliders, hence it is unrelated to engine sounds (I ignored this, thanks).
EDIT 2:
it is also worthwhile remarking what happens for high-altitude planes, when observed from the ground: in that case, the traveled distance $x$ is sufficiently large that all frequencies audible to human ears are absorbed, so that the plane goes from being nearly silent when it is approaching to being very clearly noticeable as it is receding.
You may try this on a clear day with high humidity at high altitudes, when over-flying jets leave white wakes: you will be unable to hear them as they approach (even though you can see them thanks to the presence of the white wake), but you can easily hear them as they go away, but just keep in mind that all of this is delayed by the (substantial) time it takes for sound to reach the ground, which, for 33,0000 feet or more, is of order 30 seconds. In other words, you will hear the noise level grow perceptibly about 30 seconds after the jet has passed the point closest to the observer, i.e. 30 seconds after flying directly overhead.

this is fascinating. I have always wondered about this sound change, and now I know!

There are at least three effects that can cause this
Doppler-effect
When a source of noise moves to you, you'll hear the noise with higher pitch, and when the source moves away, you'll hear it with lower pitch. This can be described by this formula, which gives the ratio of frequencies head by you and sent by the source of the noise moving with speed $v$, at speed of sound $c$:
$$\frac{f_{heard}}{f_{send}}=\frac{1}{1-\frac{v}{c}} $$
Since aircraft pass by in some distance, you can't just enter the speed of the aircraft, but this:
$$v=\frac{v_{aircraft}\cdot x}{\sqrt{x^2+y^2}} $$
where x is the horizontal and y the vertical distance to the aircraft.
I plotted this for two different speeds and several altitudes, and put the time until passing you on the x-axis:

This shows that the total shift in frequency is larger for higher speeds and that the time the sweep takes is shorter, the nearer the aircraft passes by. BUT an airliner will not fly at 1000ft with 270kt, its more 135kt.
In general, the aircraft has to fly at really low altitude to cause a noticeable doppler effect. Here is a youtube video of a landing A320, recorded near the runway.
I didn't take into account other effects like that speed of sound changes with altitude. Also Marius Matutiae meanwhile wrote something about absorption of sound in air.
Engines
Something you can observe in that youtube video, too,  is that you can clearly hear a high, screaming noise from the fans in the beginning, which changes to a dumb rumbling from the jet blast after it passed by.
Flaps
Most aircraft make some noise when deploying flaps, and I would say, the Avro RJ100 is one of the loudest airliners concerning this. The reverse effect can be heard when retracting the flaps, also from inside the aircraft (2:40)

The flaps sounds is it. I knew I'd have trouble describing the noise but it is not just the Doppler effect on the engines. Thanks for this!

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What is the bypass air in a turbofan engine actually for?
I'm planning on building a small model turbofan engine for a bit of fun but I thought I'd better get a better understanding of how they work first. I understand the majority of it at the moment but I'm struggling to see what the bypass air actually does, to my mind it seems like a waste of air and energy if its just going straight out of the engine without compression...could someone explain this to me?

From my point of view, this question is not duplicated. The question shown is actually the same principle but asking something different. This one tries to understand why there is bypass and the other tries to see where the most part of the thrust is created. However, is the same principle but different questions

Transforming the heat energy into mechanical energy??

Sorry.. I meant combustion energy..

Well the bypass air is meant to be accelerated by the the n1 fan in front of the engine. This provides about 80-90% of the aircrafts total thrust. So it's used for most of the aircrafts thrust essentially.

On modern turbojets the bypass air provides (at least) two things

Thrust
The air does bypass the engine core, but it is accelerated by the N1 fan and provides thrust as it is expelled rearward out of the engine.  Thrust from the bypass air can contribute more than half of the total thrust produced by the engine (upwards of 80% of the total thrust for some engines in certain phases of flight).  Part of the reason the bypass air is so efficient is that much energy is extracted from the core exhaust to spin the high and low pressure turbines (dual spool) that drive the N1 fan and the N2 compressor stages.
Engine cooling and noise reduction
Cool bypass air can be mixed with the hot air that went through the core at the rear of the engine.  This mixing cools the engine exhaust and reduces the jet engine noise resulting from the rapid expansion of that air once it leaves the engine.  The cool bypass air flowing around the engine core can also be used for general engine cooling.

Think of it as 80% a propeller aircraft with the  big fan acting as a propeller . The turbine part is just there to power the fan

Casey's answer is good, but @NobodySpecial, your comment would make a short, sweet, concise and to the point answer!

You're answer is quite good, however there is no rapid expansion after the engine since the pressure difference at the exhaust should not be much more than ambient to be most efficient. Also, I've never heard of the bypass air to be used to cool the engine. You might be thinking of the air going around the combustion chamber (partially creating a thin film of cooler air inside the combustor to protect it from the heat of the flame)

To achieve thrust one can greatly accellerate a small mass (fighters with straight jets or low-bypass jets) or accellerate a much larger mass to a lower velocity (passenger jets). It has to do with fuel efficiency for passenger jets (the higher the bypass, the higher the engine efficiency in this case ). I've recently learned that the exhaust velocity must be much greater for (supersonic) fighters which is why they can't have a high-bypass engine

I agree with Chris, while the second point is valid I don't think the explanation is accurate.

An airplane engine provides thrust by accelerating air (plus some combustion products) backwards. As air is accelerated backwards the plane is accelerated forward thanks to conservation of momentum.
Momentum is proportional to velocity but kinetic energy is proportional to velocity squared. The result of this is that it is notionally more efficient to accelerate a larger amount of air to a low speed than a smaller amount to a higher speed.
In practice this is complicated by the fact that the air is already moving relative to the airplane. It is difficult to efficently add a small ammount of extra speed to already fast-moving air. So the best exhaust velocity depends on the speed at which the airplane will fly.
The exhaust velocity of a gas turbine core is higher than is desirable for most airplanes. So a turbine and fan are used to capture energy from the exhaust gasses and use them to accelerate bypass air resulting in a turbofan.
For planes that spend a lot of time at low speeds, designers may use a gearbox and propeller instead of the fan resulting in a turboprop.

The bypass air is actually what gives the jet engine most of its thrust. As the air enters the engine, some of it goes to the turbine core and runs the whole engine. But most of the air goes through and is sped up by the large fan giving it the thrust. Doing it this way increases the efficiency because the engine moves more air, although at a slightly lower velocity, than just a low-bypass engine which moves some air with high velocity.

Essentially, it is more efficient from a propulsion point of view.
Let me explain this with a very simple example. Imagine that you are over a skateboard and you would like to propulse yourself using your hands to give yourself the boost.
You have 2 options, either you use your hands over another person over an skateboard or you impulse yourself using a heavy desk?
As you will imagine, if you use the other guy with the skateboard he will go in the other direction with a similar speed, and the desk will be moved slightly.
But... it is clear in your mind that is more efficient to use the desk, moreover, you will prefer to use a wall.
What is happening?
When you are trying to impulse yourself (third Newton's law) you create the same force on the other side, but when using a bigger and heavier body that body will go slower. Essentially is more efficient to "propulse" using a heavier mass at lower speed that a lighter mass at higher speed.
Is exactly the same principle that you use in water, when you use diving fins you get faster speeds as you are moving your legs slower but moving a bigger amount of water, exactly like the skateboard.
The same principle applies to turbofans instead of water they use air. Instead of diving fins they use blades.
By creating a bypass they use also the air going through the bypass to get propulsion. Is more efficient than having a single core at very high speed.

Jet planes like fighter planes have their geometry designed for supersonic speed which is  usually achieved with high velocity combusted jet exhaust from the jet engine. This consumes a lot of fuels in the high pressure compressor section.
Passenger planes on other hand are not designed to fly at supersonic speed so high velocity jet exhaust with high fuel consumption rate are not desired. The fuel optimal way to achieve this is to extract the kinetic energy from the combusted jet exhaust and transform it back into mechanical energy. This energy is used to drive the turbo fan which only compresses bypass air through the bypass section of the engine to the exhaust to achieve all the benefits of bypass jet engine as described in many other comments or articles. Note there is no fuel consumption here in the bypass section but only the excess kinetic energy of the hot exhaust is extracted and is used to run the bypass fan(s).
It is possible to design different engine mechanism to do the same thing as (high) bypass jet engine here, but it may be more complicated and has the penalty of heavier engine; therefore, less efficient than the current implementation.

I'm not aware of a single design that has a "bypass fan". Where would it even be located? You'd need some weird annular fan shape for the conventional design where the bypass flow surrounds the engine core.

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text:
What exactly is the airspace above CYYZ (Toronto)?
I'm planning my first real life cross country trip from KFRG to CYKZ. I'm trying to understand the Toronto Airspace:

Is a Canadian Class C airspace the same as a US Class B airspace?
Toronto Pearson International (CYYZ) inner blue circle has this marking 125/25 and the number 25 within a broken square bracket:

I believe this means that the airspace above CYYZ is broken into two parts: class B and class C. Does anyone know the reason for this? I have not seen this structure in the US.

The sectional for this area has the following note:

TORONTO CLASS C AIRSPACE FOR FLIGHTS BELOW AT AND BELOW 12500' MSL SEE
  TORONTO VTA CHART

I actually purchased a Toronto VFR Terminal Area (VTA) chart but it's even more confusing than the normal sectional. What exactly am I looking for on the chart?

Instead of deleting your other question and just adding details in a new question, please edit it instead.

@RonBeyer I didn't delete my other question. Both questions are still available. I just posted two separate questions because I thought putting so many questions in one question won't be wise.

Before you try to hop in VFR to a busy Class-B like CYYZ, give them a call (on the phone) to figure out the best time to arrive and the arrival method they would prefer. Nothing ticks off Class-B controllers like trying to squeeze a Cessna 172 into a busy traffic pattern unannounced. It is a little different for IFR flights, they may downright refuse to let you in VFR, so have a backup plan if they don't let you in.

@RonBeyer This is good advice. Entering Class B is not my primary option.

Canadian Class C airspace is generally the same as US Class C airspace. Prior permission is required before entering. Canadian Class B airspace is 12,500' and above. Not a factor for you most likely.
I recommend reading the VFR legend to better understand the markings. It's all there if you purchased a map. The 125/25 marking is the ceiling and floor of the airspace. What you're looking at is the US Sectional, not the Canadian one however. The square [25] refers to the control zone around the airport. You won't be landing in Pearson, so you definitely won't be in their control zone. It extends about 8nm from the airport from surface to 2500' and most busy airports have one. All control zones are class C airspace.
What you're looking for on the VTA is VFR planning. It will have recommended routes to follow, as well warnings and information needed to be able to plan a VFR flight through the area.


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How can I plan a VFR flight through controlled airspace, without knowing what instructions ATC will give me?
I'm currently planning a VFR flight from KFRG to KDOV. Due to airspace restrictions in this area, I plan to contact NY Approach and request flight following. If all goes well, then I believe I will get transferred from center to center and eventually be handed off to KDOV tower where I will land. Happy Days.
What I'm worried about is that somewhere along the way the controller will drop me with the dreaded words "radar services terminated". Say this happens between KEWR and KPHL, what do I do? Fall back on GPS/VOR? How does one create a VFR navlog for such eventualities?

I'm a little confused because flight following doesn't mean they will provide vectors and navigation, just radar separation and traffic advisories. What do you mean "fall back"? Flight following can give radar vectors but plan your flight as if you don't get them, then if you do it's nice, but if you don't it would progress normally.

In my experience this is not how it works. In this area, we contact NY approach before we enter the KISP class C or the KFJK Class B airspace. After this they tell you what altitude and heading to fly on. I can't just chose any heading or altitude. As the flight progresses they continue to give out vectors.

Under VFR you are responsible for you own navigation, radar vectors or not.

@SteveKuo If ATC gives you instructions in controlled airspace, which is likely in B/C/D airspace or E near them, you have to follow those instructions.  Approach will sometimes assign only an altitude, but sometimes they'll assign a heading too; it depends on how much IFR traffic there is and where.  Some VFR pilots avoid getting flight following (and all B/C airspace) for exactly that reason.

Short answer: make your flight plan as usual but if something changes then just deal with it. After all, as a private (?) pilot you've been trained to handle that situation.
Even an IFR flight plan is only 'plan A' and on any flight you may have to deal with changes because of ATC, weather or other issues. That's one reason why the private ACS includes a diversion task to test whether you can re-plan in the air. Note the wording of that task (emphasis mine):

Make a reasonable estimate of heading, groundspeed, arrival time, and fuel consumption to the divert airport.

It's helpful to think about general options in advance (e.g. "I'll go west around the KPHL class B if I don't get a clearance"), but you can't predict every possible situation. Always having that "reasonable estimate" for where you're going is more important than trying to anticipate and plan for every eventuality.
The good news is that as part of your original flight planning you should already have reviewed all the information you need to make decisions in the air: winds aloft, fronts, airspace, TFRs etc. So if you do have to re-plan you already have a good overview of the big picture and what your options are. "Plans are useless, but planning is essential", as someone once said.
And if you don't already have a flight app like Foreflight or Garmin Pilot then you should look into it. They make planning, diversions and replanning much simpler, which removes a lot of stress from the situation. They're also much easier to work with than paper and pencil, especially if you're single-pilot without an autopilot.
Finally, don't forget the magic word "unable". ATC can't see what you see, and they might drop you in an awkward situation, e.g. you're VFR between cloud layers and the only way to stay in VMC is to enter class B. If that happens, don't hesitate to tell them that you need a clearance, or vectors, or whatever. If they don't cooperate, you can always declare an emergency if the situation is becoming unsafe (but don't abuse the system for your own convenience).

Thank you. Those are wise words. Most of the planes here have a Garmin in the plane.

Now, the word "unable" isn't a free pass to get out of any instruction I don't like, right? I assume that saying "unable" is only permitted when I'm actually not reasonably capable of complying.

No, it's not a free pass; it's for use only when following their instructions would be unsafe, illegal or impossible.  Specifically, it's not for when you simply don't like their instructions.  Also, you need to tell them as soon as the problem is apparent, ideally when they're expecting a readback/acknowledgement, rather than (for instance) after they've vectored someone else into the space you previously agreed to vacate.

2 months after I wanted to, I finally managed to fly to KDOV yesterday. Here are some notes on the flight following experience that I hope will help other people in my situation.

Took off from KFRG and requested an early frequency change from KFRG tower ( I messed up here a bit because I had requested departure clearance towards southeast and I actually went southwest..the controllers didn't call me on it)
Contacted NY Approach at 125.7. The radio had significant static. NY Approach acknowledged but didn't respond to my request. So I circled over Jones Beach monument and call them again in a few minutes. This time they gave me vectors and altitude. I asked if I was cleared into Class B and they said yes.
I was supposed to turn left south of JFK but the controllers I think forgot about it. I went left anyway and a few minutes later the controller handed me over to McGuire Approach (124.15)
McGuire Approach gave me the altimeter. Several minutes later they said that I was on course to enter a restricted area (R-5002). I was on course from KMJX to N81. I asked the controller for vectors to avoid the restricted area and they gave me a course.
McGuire Approach handed me over to Atlantic City Approach (134.25)
Atlantic City approach handed me to Dover Approach (132.425) and then I landed
Coming back I again contacted Dover Approach on the same frequency and asked for flight following. They asked me if what my desired course was and then recommended that I fly direct back to KFRG. This may have caused some problems. I don't know yet.
Dover Approach handed us off to philadelphia approach.
Philadephia approach handed us off to McGuire approach. Since, I was now flying direct my GPS told me that I was headed for a restricted area ( R-5001 ). I was with the controller and I had told them I was flying direct. I didn't know what to do and I ended up in the restricted area. Not sure if this will cost me yet.
McGuire approach handed me off to NY Approach who again gave me vectors and altitude and then handed me off to KFRG.

In future I plan to add frequencies of approach control's along the way. This helps when there is static on the radio and you don't have to keep asking them to repeat the information. This happened a few times.

Please don't use code blocks unless you really are including code or something else that truly needs to use a fixed-width font. I changed to a quote block which looks much nicer, not to mention is actually readable.

"my GPS told me that I was headed for a restricted area (R-5001). I was with the controller and I had told them I was flying direct. I didn't know what to do" At that point personally I'd probably have contacted ATC some distance away from the restricted area (on first notification from the GPS?) to ask for clarification about the clearance. (Is R-5001 active? Am I cleared direct through R-5001?) If unable to get an answer in time, just enter a hold outside the restricted area and keep asking. Might make ATC slightly grumpy, but rather a grumpy controller than a grumpy enforcement officer!

@MichaelKjörling Thanks. Will keep this in mind for the future.

Just to be clear: I am not telling you and cannot tell you what to do. I can tell you what I would likely personally have done in a situation similar to that which you described. It's the pilot's duty to know which type of airspace you're in and whether or not you're allowed to enter other airspace. In controlled airspace, it's the pilot's duty to comply with ATC instructions when able; that sometimes includes asking ATC for clarification on instructions, if for any reason you're uncertain. It sounds like nobody yelled at you at the time, so you probably didn't screw up too badly.

@MichaelKjörling I understand. Your advice is good advice.

If you are flying an assigned vector ATC should never just drop you.  I have never been on a vector while VFR, but when IFR ATC will always tell you what the vectors are for.  For example:  "radar vectors ILS RW 16, turn right heading 070, descend and maintain 3000".  That way if you go lost comm on the vector you can take your own action to intercept and continue your own navigation to the clearance limit.
If being vectored on a departure, when ATC gets ready to "drop" you they will always do so by providing clear fix at which the vector terminates.  For example:  "maintain heading 180 until intercepting V-15, resume all navigation, .."  or:  "cleared direct SEA, flight plan route..."
"Radar services terminated" doesn't generally follow the examples above because again I am used to vectors only under IFR, but presumably you would hear that at the end if you were VFR and they wanted to "drop" you.

Yeah, my question/worries seem superfluous now. I have done some cross country flights and even though the controller got exasperated because I missed a communication they never dropped me. In an earlier life when this did happen, I was with an instructor and we were discussing/training and we missed the communication from the ATC. In that situation given that we were in the flight training zone, I guess the ATC used their sixth sense to divine what was happening and dropped us.

Most of this answer seems to be about radar vectors under IFR, whereas the question is about VFR flight following. I'm not sure how applicable your comments are.

@pondlife, read the OP’s response to the first comment.  Apparently where he flys ATC will vector VFR traffic.

First off, I don't think you can readily land at Dover since it's an Air force Base. I've asked questions about landing there as a civilian GA ppl and was discouraged from doing so. Therefore, I assume this destination is a ground school or Check ride task. In the case of a Check ride, you will most likely only fly your route for about 10-15 minutes before moving onto maneuvers. So I wouldn't worry about being dropped from Flight Following as you probably won't be picking it up.
For my Check ride I was tasked to plan a flight to Williamsburg, VA from Morristown, NJ. Although it was quicker to fly a straight line that took me near the Philly Bravo and through Alert-220, my CFI suggested I plan the scenic route by flying the coast line and try to minimize my time over water as well as have more visual reference points - like a shoreline. So you may wish to consider a different flight plan that follows the same advice.
This should work in Skyvector.com
KFRG   403305N0735621W   402757N0740021W   31E   KACY   KMIV   392100N0752116W   391840N0752646W   KDOV 
This keeps you over land longer, but of course it depends on ATC when you get clearance into JFK Bravo. Crossing over to Sandy Hook, ensuring you are above 2000 to ensure you are well out of the conservation airspace, Fly the shoreline down to Atlantic city. Overfly at above 4500 and head to Millville, then follow the small river out to the Delaware Water gap, Cross over and head south to Dover. This adds about 5 minutes, but give you shorter water crossovers where, if engine goes out, you can glide to land. Just remember your glide ratio: C172 = 9 (basically 1.5 miles for every 1000ft altitude). To cross the 6nm Sandy Hook gap and the Delaware water gap, you should be at 4500, which is the correct flight level for a south-west bound flight.

KDOV is open for public. Take a look the 'request for landing' document here(http://www.catatdover.com/forms.aspx). It is used heavily by NASCAR followers in summer and fall. No, it is not a checkride task either. I actually plan to fly there :)


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When do controllers assign a squawk code to VFR aircraft in Canada?
In all of my previous flying experience the controllers provided a squawk code only when I requested flight following. On a recent flight from Buttonville, Ontario (CYKZ), the controller provided a squawk code on the ground. I asked if she was providing a squawk code because she was going to provide flight following as well. She said the flight following will need to be requested after she hands me off to Toronto City Center.
Then why was the squawk code provided? Was the controller anticipating the need for a squawk code? Are all airports in the Toronto region required to provide squawk codes to departing flights?

I almost always get a squawk code departing from/arriving at my home Class-C.

Are you asking about Canadian rules or US/FAA rules. You flight appears to cross borders, jurisdictions and rule sets so you may wish to specify for a better answer as the various jurisdictions may handle this differently.

@Dave I am asking for the Canadian rule.

@PrashantSaraswat I'll leave that for someone else I can only answer for the FAA side of things

The controller will assign you a squawk code if they want to differentiate your radar return from other aircraft. It has nothing to do with whether you're getting flight following or not. If they're happy they know which blip is you for the length of time that they'll be watching you, then they may not give you a squawk. In some airspace, the moment you begin talking to them then they'll give you a squawk. All depends.

you are right. It looks like it is at the discretion of the controller. The squawk code gives them more visibility and control.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


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What happens when changing the throttle on a PT-6 engine?
Imagine a PT-6 in cruise flight. What would pushing the throttle forward for increased power show on the engine instruments? We know (I assume!) the prop RPM remains constant by varying the pitch, but what goes higher? Torque or TIT?
And what does the pilot do in descent for landing? Does pulling the throttle back for a long descent decrease the fuel flow to a point where it may not sustain combustion and cause flame out?


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For how long can a single-engine turboprop safely run the engine at idle?
Can a single engine turboprop (such as a Piper Meridian or TBM) allow idling long enough to drop off a passenger or package without shutting down the engine? If so, would the prop be feathered but still spinning? Would idling with the prop not spinning (if possible) hurt the engine?

The question one should be asking is whether they want to incur the risk of someone running into the prop on a package or passenger drop off.  The issue is really a best practices issue.  However, I seem to remember the factory commenting on extended idle times for the PT6-67A but I lack any documentation on that.

It's not stressful at all for a turbine engine to run at idle, you could run it until the fuel runs out. The prop is not feathered (in line with the air stream, pitch 90°) but will be at ground fine, in line with the direction of blade turn, pitch angle 0°.
There is usually no way to disconnect a propeller from a single spool turbine engine: if the engine runs, the propeller turns.

With the prop turning relatively slowly, you can always feather it, with the blades in line with the air stream, but not at a pitch of 90º, but somewhat less... In that way, drag will be minimized...


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How did the F28 have such a good L/D ratio?
The second link given on a Google search for "Breguet Equation" is to a PDF document from MIT.  On page 7 of this document is a chart showing L/D ratios for various commercial aircraft (turboprop, regional jet, and "large aircraft") plotted against the year the aircraft entered service.  Below is an image of this chart:

What appears to stand out (at the top of the chart) is the Fokker F28 aircraft.
From an engineering and operational perspective, what enabled that aircraft to have such a high L/D ratio?
Also, I thought that the F50 / F70 / F100 aircraft had the F28's wing (or an evolutionary version).  Why didn't these aircraft have an equally good L/D ratio?

The F 50 is a development of the F-27 and has a different wing.

@PeterKämpf:  Thanks, corrected.

Taken as I am with the little Fokkers because I used to walk around the flight line and see them being built, I reckon that's a mistake. The F-28 having a better L/D ratio than the F-27 with its long slender wings doesn't sound right to me. The F100 with its supercritical wing definitely should have better L/D than F28.
The two entries for F-28 in figure 1.4 seem very similar to the entries in Figure 1.9 of the MIT document that you mention.

The supercritical wing only helps at higher Mach numbers, but the F 100 had a higher aspect ratio than the F-28, so I agree with your verdict. The low sweep angle helps in comparison with other jets, but not enough to make the graph look credible.

I agree with both Koyovis and Peter... The data look suspect.  Of course, the horizontal locations of aircraft are the same on both charts (x-axis is year of introduction in service).

Indeed. The y-values seem similar as well.

A little like comparing Vmin sink to Vbg, no?

They just got this wrong. I have flown F28-1000 and -4000, the F100 and the B767-300. The most feet per nautical mile lost of these with idle power at any given Indicated Air Speed (say 270-280 below 25000 ft) is the F28-1000 (around 475 fpnm) then the F28-4000 at about 425 fpnm, then the F100 at about 350 fpnm and the best is the B767 at about 300-330.The 425 fpnm figure for the -4000 was measured by me around 2004 to get data for MS Flight Sim. All the rest are educated guesses.

There is one possible explanation in the analysis of the airfoil and the airspeed it is flown at.  A cambered wing, such as the Davis or the DAE-21, will produce superb lift to drag ratios, but at much lower airspeeds than supercritical wings fly at.
The Breuget Equation is as follows:
Range = Velocity × Lift/Drag x Specific Impulse × ln(W2/W1)
Specific Impulse is Thrust/fuel flow rate, Weight = Lift, Thrust = Drag, therefor:
Range = Velocity × Weight/fuel flow rate × ln(W2/W1).
The faster, heavier plane with the lowest fuel flow rate becomes "tops of the charts" in any year.  The graph, though interesting, seems to only point out the F-28 lifts more weight/drag at the speed it flies at per given unit of time, but not per given mile.  I would ask more of MIT.


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Why is the GP7200-powered A380 fleet not grounded?
After the Qantas A380 engine failure, all Trent-powered A380s were grounded.1
After the Air France A380 engine failure, the GP7200-powered A380 fleet was not grounded.
Why were these two incidents handled differently? And what are the primary drivers for grounding a fleet?

The one that decided to ground the fleet was Qantas. Qantas was having a new airplane model and potentially made a trade-off between having a not known design flaw and keep flying and the risk. At that time the A380 entered in service three years before and around 20 aircraft were in service with a mix of engines.
Today, there are 200 A/C in service for 10 years. The possibility of having a design flaw or an unknown problem is really low.
It was not a airworthiness directive as the directive was created 2 months after in January 2011. Qantas starting to get back in service the airplanes on 27th November (incident was on 4th Novemeber)

It depends what the root cause was (and we don't know yet, for the GP7200 incident). For example, a fundamental design flaw is one thing, but some klutz mixing up the part numbers and using the wrong type of bolts or the wrong torque setting when maintaining a single engine would be no reason to ground the entire fleet - just check the bolts on everything the klutz might have touched recently! Even though no information has been released, its quite likely that Airbus and the EA have a pretty good idea of the cause within hours of the plane landing.

... failures like this look spectacular, but the root cause might be quite simple, and you can learn a lot very quickly from a video link up (over a secure communications link!) between a roomful of specialists at Airbus and EA, plus somebody on the ground operating a hand-held video camera - and the major manufacturers have the systems in place to provide that level of technical support 24/7/365.


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Can civil pilots *ever* fly military high-altitude penetration approach procedures?
Let's say I'm flying some business types in a Gulfstream III (an approach category C aircraft) from Stockton to Palmdale to meet up with some USAF types there (new airplane deal, wooo!).  Can I accept/fly the HI-ILS approach to RWY 25 at KPMD:

or am I only allowed to accept a STAR or vectors to a standard ILS approach to KPMD?

As long as you can actually make the altitude restrictions, then yes, there's no reason why you cannot request to fly the approach.  However, as a general courtesy, you should also factor in your approach speed.  ATC might not appreciate a Cessna clobbering the approach 34 miles out.  These approaches are typically flown at 250+kts, so just keep that in mind.

Depends on the Cessna -- a C172 would fly the ordinary ILS, but a C550 might fly the penetration procedure ;)

Might check what descent rates would be required before trying it with passengers, but there shouldn't be any reason in principle that ATC couldn't clear you for that version of the ILS there.

authors: Оскенбай Момынов


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Was the unmanned flight and landing of the Buran spacecraft in 1988 exceptional?
The Buran had a very sad fate. But in 1988 it has undertaken its first and last flight, which was unmanned and landed with a precision of three meters in a crosswind of 60 km per hour. It lost only 8 of its 38 000 thermal tiles.
What was the level of technology of automated flights in that times? Was it usual that airplanes landed automatically or was that flight of the Buran something like exceptional?
Here is an image of the Buran with Energija launch vehicle:

(source of the image)

V-2 rockets have been very accurately positioned since WWII. Automatic landing systems have been in development since 1945 and in use commercially since before 1975, so I'm not sure the automatic landing of the Buran was exceptional...

@mins For 1944 without INS and modern systems, 12km is still pretty accurate :)

@mins You are correct, I was thinking of something a little more modern like solid state AHRS. Still think 12km is accurate given that manned powered flight itself just came into being 35 years prior.

@user3624251: On the contrary, there are many spacecraft that have done unmanned landings.  Granted, most of them were on other planets (or moons, asteroids, &c).

That crosswind figure just keeps going up and up and up.  In reality, from the videos available, it's clearly much less than 60kph.

@RonBeyer: The neural network used on the Buran FCS was certainly exceptional, also the fact that it commanded a second approach on its own. The crosswind would had been 60 km/h on the first landing attempt.

Your question is very subjective, but I think there are two ways to look at it:
Building a working space plane is pretty exceptional.
or
There's really nothing it did that wasn't done by something else.

The NASA shuttle was flown in fully-automatic mode for launch, and most of reentry. It's also the vehicle which pioneered the thermal tiles, the reentry profile of a space plane, and the general concept of a shuttle. Buran could almost be thought of as an iteration on that design. The Soviets used some lessons learned and, in some respects, built a better shuttle. Does that in itself make the Buran exceptional? Probably not.
The only thing Buran really did that the NASA shuttle never did was fly unmanned, including an automatic landing. That seems to be at the heart of what you're asking, so I'll address that specifically.
Autoland had existed for decades before Buran, so it certainly wasn't the first airplane to land on autopilot. Although, it may have been the fastest autolanding to date, which could be an argument for exceptional.
I would note that even though there was only one orbital flight of Buran, there were atmospheric tests of prototype vehicles (some prototypes had jet engines), so there were opportunities to safely test the autopilot during the landing phase of flight prior to the orbital test. In fact, it would have been the only phase of the autopilot that saw real-world testing prior to launch. So once Buran got on approach, the fact that landed safely probably shouldn't be too much of a surprise.
Lastly, I've heard and read many times how amazing it is that Buran landed so close to centerline in such a dramatic crosswind (around 33 knots). I think that would indeed be pretty impressive... if it were true. However, I urge you to go look at video of Buran landing (example, mute recommended). Does that look like a 33 knot crosswind to any pilot? To me, it looks like about a 5-10 knot crosswind at most. You see the wings doing very little correcting, and the wheels touchdown at almost the same time, which is very much not indicative of a crosswind.
For comparison, take a look at STS-133 landing. Note the wing movement at 8:58 which is to correct for about a 12-knot crosswind gust, which looks about right to me. Notice how the upwind wheel hits the runway about a second before the downwind wheel hits - very indicative of a crosswind.
I have no idea where the crosswind number came from, but it was almost certainly exaggerated, either on accident (perhaps mistaking wind conditions on approach for surface wind), or intentionally exaggerated to show how great and superior Buran was. Either seems plausible to me.

I tend to be in the camp that says anything you build which successfully goes to space and comes back safely is pretty exceptional, but I wouldn't say Buran was a tremendous advancement over existing technology, and ultimately it's always going to be difficult to really assess a ship which only flew once.

Not to mention much of the Buran design was "copied" from data provided by NASA and the US Government on the Space Shuttle program. The VPK/KGB had an entire department of people that would photocopy design data. Its a good read if you have some extra time

@RonBeyer The way Bret puts it is IMHO pretty much spot on. While the Soviets used the Shuttle as basis the differences were too large to really "copy" anything. For example the thermal tiles while in theory the same as in the Shuttle, actually were different in attachment and organization. While the launch was similar it was actually different because Russian launch systems were quite different. While landing solution was the same it too would have been different in practice. One question relevant difference is that it was specifically designed for remote and automated control.

@RonBeyer I've read that article before, but I think the significance of the espionage has been largely overstated. Both shuttles were built with very similar goals and requirements in mind, so the fact that they look and function similarly is to be expected, just like how large commercial airplanes with similar capacity and range requirements often look remarkably similar to each other - or, at least as similar as the NASA and Soviet shuttles look to each other.


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What are the major differences in operating the Boeing P-8 Poseidon and Kawasaki P1 in the maritime patrol aircraft role?
What are the advantages and disadvantages of the P-8 Poseidon and Kawasaki P1 in the maritime patrol aircraft role? They were made for the same role, but they are different. The P-8 is something like converted from a civilian design while the P-1 is military-purpose built. What does that mean? What does the different number of engines mean for missions undertaken by these aircrafts?
P-8 Posiedon (left) and Kawasaki P-1 (right)

(source)

One is japanese the other is US. That's enough of a difference for some.

And what is the advantage? To be american, or japanese?

@user3624251 I think what ratchet is saying is that the P-8 is used by the US, and the P1 is used by the Japanese. Are you just asking what the differences are? Because I don't think there is much of a choice about which one is used for a particular country...

I am not asking on the difference. I am asking on advantage and disadvntage. One has two engines, one has four, one was built as a military plane, the other was built as a civilian plane. I do not know what these think make of an advantage and what not. That's why I am asking, because they were made for the same role, but they are different.

I think this is too broad, you are asking us to go through every difference in the aircraft and provide the advantages/disadvantages. If you can pick out specific things it would be more on-topic, but as its written its far too broad to answer.

From the beginning, i picked up two differences. For example that one was built as a military plane from scracth, while the second was not.

Roughly 2 engines.

Four engines is more survivable with respect to birdstrike damage than 2, a serious concern for an aircraft that will spend a great deal of time at low altitude hunting submarines.  The P-8 lacks a magnetic anomaly detector and may not have any reason to fly at low altitude.

Both the aircraft were designed as replacements for the Lockheed P3C Orion when the P7 was cancelled. While the USN decided to convert a civilian aicraft (as is the norm for most MPA), the Japanese decided to design theirs from scratch (the aircraft was supposed to share a number of items with Kawasaki C2, which given the wildly different mission requirements, didn't go very well). Almost all the differences between the two aircraft, which share a number of similarities resulted from this differing approaches to design.

The P8 was derived from 737, a commercial airliner, which means that it is optimized for high speed, high altitude flight. Previosly, the MPA were optimised for low altitude operations. The P8, on the other hand has (relatively) highly swept wings with raked wingtips, optimized for high altitude cruise. This means the development of modified operational procedures for this aircraft.

Image from ainonline.com
The P1, on te other hand, is purpose built to be a more or less a one-to-one replacement for the P3C, optimised for low altitude operation with strnthened structure. The wings are swept less and the wing area is relatively more compared to the P8.

Image from battlemachines.files

Operating the aircraft at high altitudes instead of lower ones also means that the operating principles are different. It is the main reason for the P8 not having the Magnetic Anamoly Detector (MAD), which was available in P3C (as well as P1, in the long boom in the tail). Last heard, UAVs are being developed with MADs to overcome this issue.
The P1 has larger windshields (which makes sense, as the crew would be able to scan better for ships at lower altitudes) and more hardpoints compared to the P8.
The P8 has only two engines compared to the four of P1, a significant difference. For aircraft operated in long stretches over areas without airfields, this could be a real issue. While so far no issues have been encountered in this regard, the loss of an engine in a P8 is basically a mission kill, which is not an issue with the P1.
The from-the-scratch development of the P1 alos has enabled the use of fly-by-light controls, which is a first for operational aircraft, allowing for lighter wiring and lesser interference.
One significant advantage of the P8 over P1 is that being based on one of the most successful and widely operated aircraft in history, spares and support will not be a big issue.

Is the lack of MAD a big issue for a MPA? If there will be no unmanned plane in the area, what does that mean? That the P-1 would be ble to detect a subamirne while the P-8 not? I also notest that the nose of the P-1 is much bigger. Does it have a stronger radar?

@user3624251 - The MAD is a very short range sensor. You need to be kinda lucky for a MAD hit. You have to fly directly overhead a target at low altitude to find him. Even then, some subs are made from non-magnetic steels (eg, German Type 212, Type 214) or titanium (Soviet Sierra, Alfa, and Papa class SSNs, portions of the Typhoon's 10 pressure hulls). Magnetic silencing and diving deep will also reduce/hide a sub's magnetic signature. Wrecks in shallow water will also show false-positives (but these are often known and mapped). Basically, MAD isn't crucial for hunting subs.


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How is the Angle of Attack influenced in the slipstream of a propeller?
My question is how can the angle of attack be changed when the wing is in the slipstream of a propeller, giving "enough air flow" to the wing. The propeller sends the flow of air in the same direction related to the wing no matter how the aeroplane is oriented in the space. So theoretically the angle of attack should never change.
UPD: The answer should not depend on how the plane is thrusted. Turbo engines are also pushing the plane in the same direction related to the fixed wing. ( I am not talking about engines that can change the vector of thrust).

Hello Boris, welcome to Aviation.SE!

Possibly related question http://aviation.stackexchange.com/questions/9543/turboprop-wake-over-wing/9553#9553

Not all planes have propellers and not all of the wing is behind the propeller.
In fact only a small part of the wing is behind the propeller. The rest will get clean air depending on the attitude (orientation) of the aircraft. The wing is also not perfectly straight behind the propeller either, usually dropping down a bit so there is a positive angle of attack.
Jet powered planes generally have their engines away from the wings.
In most planes, thrust is surprisingly small compared to the weight, an empty A380 only has a thrust to weight ratio of 0.47 and most of that thrust will be applied horizontally. So as the plane will sink rapidly should there be no lift from the wings. That sink tendency is what provides the angle of attack.
This will max out the sink rate should the wings be level, angle them up a bit and the plane will try to climb.

The answer should not depend on how the plane is trusted. Engine are also pushing the plane in the same direction related to the fixed wing.

I believe that the question is about the washing up the top side by the way that's the airflow is formed behind that portion of the wings.

The angle of attack, in relation to a propeller, probably affects yaw more than anything.
The way a plane is thrusted, propeller vs jets, significantly changes the dynamics of how the plane flies.  Because of propeller torque and p-factor the plane tends to yaw more and will require more rudder input to compensate, especially as angle of attack is increased (on take off for example).
Look at this link to P-factor for more information.  Here's an excerpt:

P-factor, also known as asymmetric blade effect and asymmetric disc
  effect, is an aerodynamic phenomenon experienced by a moving
  propeller, that is responsible for asymmetrical relocation of the
  propeller's center of thrust when aircraft is at a high angle of
  attack. This shift in the location of the center of thrust will exert
  a yawing moment on the aircraft, causing it to yaw slightly to one
  side. A rudder input is required to counteract the yawing tendency.


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Does Part 135 allow single-engine night IFR operations in a turboprop?
Do the Part 135 rules allow single-engine turboprop night IFR Part-135 operations? If not, then all the night activities of current popular (and expensive) single-engine turboprops are by private or corporate owners and there are no commercial operations...!!!
I understand certain single engine turboprops are allowed to fly IFR at night for hire in EU, but I am not sure about it. Your input is much appreciated.

Do the Part 135 rules allow single-engine turboprop night IFR Part-135 operations?

Yes, there is nothing preventing it provided the pilot is night current and the airports are suitable for night operation.
You can find the FAA's 135 general requirements here.


text:
How precisely are airspace borders defined?
I'm studying for the commercial drone certificate. In Tucson, AZ the class C airspace covers about half of the city, but the charts don't list the exact point that it ends. Here's a portion of the VFR chart:

How exact are these airspace borders? Could one city block north or south get me in trouble if I don't check in with ATC?

Welcome Mitch! Areas are defined using their geographical coordinates. So it's exact. What is the airspace you are asking about?

davis monthan afb class c

When in doubt or close, call Tower and state your intentions.  They'll approve you, and if you cross into their airspace you will be legal.  If you stay outside their airspace, you asked approval for no reason, but no harm done.

The boundaries are defined more precisely than the chart can show. What you see on the chart is a visual representation of the text published in JO 7400.9Z (or the most recent version of it):

AWP AZ C Tucson, Davis-Monthan AFB, AZ
  Tucson, Davis-Monthan AFB, AZ
  (lat. 32°09'59"N., long. 110°52'59"W.)
  Tucson International Airport,
  AZ  (lat. 32°06'58"N., long. 110°56'28"W.)
That airspace extending
  upward from the surface to and including 6,600 feet MSL within a
  5-mile radius of the Davis-Monthan AFB to the points where the 5-mile
  arc joins a 5-mile arc from the Tucson International Airport, AZ,
  Class C airspace area, and that airspace extending upward from 4,200
  feet MSL to 6,600 feet MSL within a 10-mile radius of Davis-Monthan
  AFB to the points where the 10-mile arc joins a 10-mile arc from the
  Tucson International Airport Class C airspace area.

So in theory, if you're at 5 miles and 1 foot from that lat/long point then you're outside the class C's inner area. But the chart has to show that information in a way that's usable for practical purposes, which means that there has to be a visible line on the chart and that line has thickness. It looks to me like the airspace boundary lines on the chart are roughly 0.25nm or about 1500ft thick, and I have no idea where the boundary really lies on it. You simply have to consider that as a 'margin of error' in this case and plan accordingly. If in doubt, definitely contact ATC.
As for getting in trouble, 1500ft is probably too close for comfort for a manned aircraft, and ATC reacts on what they see on their radar, not what you see on your GPS. It's an interesting aspect of this question that you can probably be more precise with a UAV than a manned aircraft, and 1500ft might seem like more than enough buffer for you. But again, if you have any doubts or questions I would ask ATC directly.

Here is a map based on the above description which shows the inner areas on a map that you can have satellite view on and zoom in to street level (note that in this JO, "miles" refers to NM).  (I'm assuming that the outer areas won't be needed since the drone will have to fly below the altitude of the shelf.)  The accuracy is limited to that of the map itself.

Also, that JO is accurate as of July 28, 2015.  If you need current data, read the JO and it has a link to changes since that time.

The airspace is defined by a written publication.  Most likely, for this Davis Monthan Class C airspace the definition is based on the 5 and 10 NMi rings from the published, and surveyed, airport reference point (this could be the control tower location, for example) on the airport master record.  For example, you can find one point here:  DMA Airport Master Record
There is survey accuracy data, but I don't think that is really the point of your question.  The answer is that as far as the FAA is concerned that 5 NMi ring is THE airspace definition and your UAV is either in it or not.  There isn't a "grey area" of "kind of in it.".  So, one side of the block is 4.95 NMi, and is in the Class-C, while the other side, at 5.02 is outside.


text:
Are the captain's and first officer's brake pedals always mechanically linked?
I heard that for Boeing and Airbus aircraft, the pilot's and copilot's brake pedals are mechanically linked, is that true?
Why did they make that design decision? What's the advantage? Do all kinds of passenger aircraft have the same design?

More like hydraulically linked? What else can you do so that they can both operate the brake? Use full electric control? Two independent brake systems?

@user3528438 The planes are fly-by-wire so they certainly dont need a physical link between the controls. For a specific example, the sidesticks used to control Airbus aircraft aren't physically linked, which was a factor in the crash of Air France flight 447.

It is cost effective for one. With an unlinked system, you now need to resolve disagreement between inputs some other way. Software has its own challenges. It's also instant, non-verbal communication between captain and first officer. A pedal moves and the other's pedal has already moved. No confusion or pilot effort to communicate it.

Yes they are always mechanically linked. It is the best way of having two persons operate one device, since both can feel what is happening without having to look at what the other is doing - they cannot see each others' feet anyway.
The force sensors in our body are quite accurate and can intuitively interpret if someone is helping or opposing in actuating the task at hand, because this is how things work in nature and that is what our bodies are built for. In nature, an item moves as a result of the sum of all forces. So best to build a set of brake callipers such that it is deflected as a result of the sum of forces of the two pilots, in such a way that each can feel what the other is doing.
Mechanically link the captain and F/O brake pedals and:

When one pilot deflects the brake pedal fully, the other one can feel the pedal being at the travel stop and knows that further pushing has no effect
Each pilot feels the brake pedal deflect as a result of the others action. If #1. wants to add to the action of #2, #2 can feel that instantly.

Is this true for Airbus too? Seeing as their sidesticks are not mechanically linked.

I assume so but cannot find confirmation. The A320 simulator Level D flight controls I worked on had mechanically interconnected rudder pedals, and it seems logical that the brake pedals are mechanically interconnected as well. I'll check next time I'm in the sim.


text:
Should I land a Cessna 172 with or without a little power?
Cessna 172 landings with full flaps. I have been taught to land with and without power. Give me feedback please. Which way should I continue my training?

Without.  It's so light that even a little power will use more runway than you'll really need.

@acpilot  I have never flown that plane, and I'm not sure, but with very light planes, the problem of using full flaps is that the high drag may slow the plane too much in a very short time (due to the low mass of the plane) and if the pilot  is landing without power and gets distracted for a fraction of a second, he may find himself below the stall speed...

@xxavier, flying a 172 is nowhere near that intesne.  If a pilot finds himself in the position you describe, he's doing it wrong and needs remedial training.

This is really a question for your instructor: if you've been taught both methods then he should be able to explain when to use a little power and when not to.
Having said that, it all depends: there are good reasons to land with and without power, depending on the situation.
A normal landing with full flaps in a 172 is typically done without power. The Cessna 172S POH I have doesn't even mention power in the normal landing procedures; it gives a target airspeed instead.
A short-field landing is also usually without power, to minimize the runway distance needed. The same POH says:

Power -- REDUCE to idle after clearing obstacle

For a soft-field landing on the other hand, it's normal to carry a little power in order to touch down as gently as possible and avoid sinking into the runway surface. The FAA's Airplane Flying Handbook says in Chapter 8:

Power is used throughout the [soft-field] level-off and touchdown to ensure
  touchdown at the slowest possible airspeed,

Finally, you might also use a little power if you bounce on landing, to stabilize the aircraft and re-flare (runway length permitting). But that's a bit more challenging and most low-time pilots should just apply full power and go around instead.

As a 172 pilot I cannot think of any normal cases where landing with power would be a good idea as any power will extend the landing distance significantly and extend the float and hold-off. In a normal landing I might add burst of power if the sink rate gets too high, but I would always cut it off as soon as I reach ground effect.
Throttle is used in short/soft field landings which are at the edge of the performance envelope. These are done at low speed and high drag, the throttle is needed to keep the airplane above stall speed and force air over the tail's control surfaces so you maintain control. You keep the throttle on in the flare until you reach your touchdown point and then you gently close it, and the airplane stalls onto the strip.
So as you continue your training you should practice both techniques as each has its own purpose, and you should keep practicing both after you get your licence. Just keep in mind that the short/soft field technique has much less room for error, so make sure you know what you're doing!

I can think of a situation where I'd carry some power (and more speed) on final: a field with a steep dropoff on the approach end, where a good headwind might produce a downdraft.

I'm not saying not to have power on final, I'm talking about power on the roundout and flare @jamesqf. Extra power on roundout doing downhill in a 172 will give you a lot of float.

It depends. You should not be afraid to use whatever power setting is necessary to maintain a proper glide path. Especially with full flaps, when you get low and slow you might need a lot of power.
The answer about the Soft-Field and Short-Field landings is excellent, and goes to the point that "it depends."
I looked in two POHs.
The POH for a 1981 C172RG doesn't mention whether normal landings should be done "power-on" or "power-off", which to me means it is my option.
For comparison I also looked at the POH for a 1979 C152, which says, "Normal landing approaches can be made with power-on or power-off...."  However, it says that "actual touchdown should be made with power-off and on main wheels first."
I was taught to always keep my hand on the throttle during landings and use as necessary.

Are you referring to a power/unpowered approach, using power during the flare, or using power as the wheels touch the ground?
A few considerations (without giving an actual set-in-stone answer)
On approach:
1) approaches without power (commonly called "dead-stick landings) are OK, but if you end up just a little short, it's a bad time to discover that your engine has stopped during that descent. At minimum, give it a little power periodically to confirm it's still responding.
2) cutting power at altitude and gliding the whole way down introduces a lot of cooling (less heat from combustion and friction within the engine combined with increased airflow). Most (but not all) agree that rapid temperature changes reduce engine life.
3) from a speed perspective, maintaining a cruise descent from several miles out will get you there faster than cutting the engine closer and being limited by Vno, Vne, or RPM (which will still be high on a fixed prop aircraft with the throttle at idle on a steep descent)
during flare and touchdown:
1) with more flaps and less power, your approach angle will be steeper. With power and a lower flap setting, the shallow approach angle will be more forgiving for newer pilots who are still fine tuning their flare and touchdown. I had trouble getting really smooth landings with full flaps and no power, and found that with lower flap settings and a tiny bit of power, I'd hear the wheel bearings spinning before I felt the landing. This can be useful for a student to gain more spatial awareness of the height of the aircraft over the runway, and can be a good stepping stone into greasing perfect landings in any configuration.
2) of course, more flaps and less power lead to a shorter ground roll. So don't have a crappy approach and run out of runway.
3) keep in mind that your landing configuration will change depending on situation, and being able to adjust to the situation is very important. 30+ flaps in gusty crosswinds can create more problems than the solve, and tailwind landings with full flaps can be interesting as well.
Source: c172 owner, commercial / instrument rated, skydive pilot (in c182 and other airframes)

Re "discover that your engine has stopped", or discover that pushing in the throttle too quickly causes it to stumble and almost stall.  (Been there, done that, had to clean the seat afterwards :-))


text:
Is this legal for transportation in the US? (video in description)

I wanted to make something like this, but I don't know if this is legal for transportation.

What kind of transportation? Anywhere through the air?

Related

In class G airspace provided proper separation from people and buildings you should be good to go. The airspace you are in can be determined by geographic location and altitude using the FAA's charts you can find here.

legal for transportation.

This is a somewhat broad term. The FAA may require you to get it set up as an experimental aircraft but thats up to them. If you plan to do more than hop around empty farms and over a pond you may want to contact your local FSDO for a ruling on what you can do. You can also reach out directly to the FAA for a ruling on a specific question.
The FAA as per

§ 1.1 General definitions.
....
Aircraft means a device that is used or intended to be used for flight in the air.

does define what you show as an aircraft and would most likely see it as falling under their purview.
Note that since he is over open water he has a life jacket on board (although he is within the required 50 miles and technically does not need one). He also has a chute presumably for emergencies.

You might want to add the altitude limits that apply to aircraft and the airspace classes.

I think there's a pretty good chance that the FAA would classify it as an ultralight, not an experimental aircraft. In that case, part 103 would apply, not part 91. But that's all speculation until/unless someone tries to operate it in the US.

Why do you say class E airspace? Generally things like drones and ultralights, are banned from class E

Mostly because you dont need a radio to enter but I was unaware ultralights were banned from E, I will update to reflect.


text:
Is it required to report climbs and descents within a block altitude assignment?
The following is assuming US FAA and IFR.
This question stems from a question on CRUISE clearance. Section 4-4-3.d.3 of the 2021 AIM says that in a CRUISE clearance

Climbs/Descents within the block is to be made at the discretion of
the pilot.

I've never been given a CRUISE clearance, but I have been given a Block altitude assignment before (e.g. 8000-12000). I could climb and descend to my heart's content without telling ATC every time I changed altitude within my assigned block. In fact, I've been voluntarily given a block altitude assignment by ATC just to shut me up after asking for too many altitude deviations for weather.
The AIM says about CRUISE clearance,

However, once the pilot starts descent and verbally reports leaving an
altitude in the block, the pilot may not return to that altitude
without additional ATC clearance.

Some of my fellow pilots interpret this to mean that you must report to ATC when you descend, but the way I read this is that you don't have to report leaving any altitude in a Block until you are finished with that altitude or the block, and once you descend AND report leaving an altitude, then that signifies to ATC that they can assign that vacated altitude or block to other aircraft. However, none of this appears to says to me, that you have to report descending within the block if you intend to climb back up in the block later.
In other words, don't report to ATC that you're descending until you are done with the block. For example, if I'm given 8000-12000. And I start my final descent and I know I'm not going to be climbing back up then I'll tell them Cessna 123 10000 descending 8000. Then ATC can assign the 10000-12000 block.
Questions:

When given a CRUISE clearance (which includes a block altitude assignment from MEA to CRUISE altitude) where does it say that a pilot must report altitude changes (climbs or descents) within the block altitude. If not, then where does it say you don't have to report altitude changes.

Is there an FAA publication that provides more information on Block altitude assignments and Cruise clearances besides the AIM?

When given a CRUISE clearance [...] where does it say you don't have to report altitude changes.

In my opinion, it say that by implication in the text you quoted, emphasis mine:

The pilot may level off at any intermediate altitude within this block of airspace. Climb/descent within the block is to be made at the discretion of the pilot. However, once the pilot starts descent and verbally reports leaving an altitude in the block, the pilot may not return to that altitude without additional ATC clearance.

I read that to mean, and as a controller I was taught that that means, you can climb and descend to your heart's content while operating on a cruise clearance. Only once you report leaving an altitude are you required to remain below that altitude; therefore by implication you are allowed to return to that altitude so long as you don't report leaving it, and therefore by further implication you are not required to so report in the first place.
The AIM references the Pilot/Controller Glossary term "cruise" which contains the same exact verbiage.
The 7110.65 contains instructions to controllers that further this interpretation, particularly 6–6–2c under the Non-Radar section and 5–6–6a under the Radar section, which say that controllers cannot use Mode C altitudes to guarantee vertical separation if one of the aircraft involved is on a cruise clearance—because the aircraft is allowed to climb or descend without notice.

so it sounds like you agree with my interpretation? As a controller, when you assign a block, the entire block belongs to the pilot until the pilot gives it back by verbally reporting leaving an altitude within the block or the entire block-is that a fair assessment?   Thanks for the reference to 7110.65.

@Devil07 yes, I would agree with you.

@Devil07 it is also important to distinguish between a cruise clearance and a block altitude clearance—but in either case I would not personally expect a pilot to report maneuvering vertically.


text:
How is metal fatigue detected in an aircraft?
There have been many accidents involving metal fatigue. How do the engineers, maintenance team, etc. know if an aircraft has metal fatigue? What is done to "minimize" metal fatigue or repair it?

On a side note: I used to work in the field of nuclear safety. We used a piece of very sophisticated and very expensive software for predicting an outcome of a ultrasound test of a piece of piping. A significant portion of that software comes from Boeing (not a software company). There are very interesting and hugely sophisticated methods available and are continuously developed within the industry, that are not visible to us passengers, but contribute a huge deal to the overall safety which we do care about.

I know that you were asking specifically about metals, but if this was a question of curiosity you should look into new techniques for composites. These are being used in increasingly large percentages of components in aircraft, and need a whole new set of hardware to assess fatigue. I found carbon fibres pretty interesting- give it a look!

@Pavel Hmm.. do Boeing have an in-house software team then?

@Cloud Can't say, really. I remember seeing Boeing in the copyrights and acknowledgements.

How do the engineers, maintenance team, etc know if an aircraft has metal fatigue?

First of all, is not an "aircraft" that has fatigue, but a component.
To the naked eye, there is no way to detect metal fatigue until it starts being too late: you can only see cracks that are already forming and/or propagating.
There are tools available to allow for early detection, my bachelor's thesis was about one of these: the photoelasticity of certain materials is used. A light coat of one such material is applied on the new component and the photoelastic properties and exams done during the lifetime of the component tell the maintenance people what is the current status of the inner layers of the piece.
Another method uses electric resistance, as metal fatigue, by cracking the metal, increases the resistance.
Depending on the scenario, X-rays could also be used.

What do they do to "minimize" metal fatigue or repair it?

You cannot minimize fatigue, once it starts setting in, it is an irreversible process. You can delay the likely catastrophic failure by applying strengthening elements around the affected one, but the safest course of action is to replace the component and recycle the old one.

And, of-course, they do stress tests of the separate components giving the manufacturer an indication about when metal fatigue will start to become a problem. They know when to look and where to look based partially on those tests.

First of all, is not an "aircraft" that has fatigue, but a component. - While this is true it's notable that sometimes the "component" in question is in effect the whole airframe. Consider Aloha Airlines flight 243, where widespread metal fatigue in the skin was a key factor. We can of course view the skin as a component, or even a collection of components (the individual sheets of aluminum), but for practical purposes the whole aircraft is affected as a unit.

@voretaq7 eh, this is where I let my engineering take the best of me. Yes, as you say I would still consider the affected frames or skin panels as components, since, if caught early, you could still think about replacing them. Plus, it drives the idea that you have to observe each component on its own, no fatigue on the skin is no guarantee of no fatigue anywhere else.

Years ago, I used to work for an aircraft manufacturer who started getting fatigue cracks in components that according to all the data, should not have been occurring that early.this was in a test airframe that they cycled with load for just such unexpected circumstances. After much investigation they found it was due to two components that were bolted together of different materials having slightly different resonating frequencies. At certain engine speeds, the difference in vibration set up a harmonic which added way more load than was expected and caused the fatigue.

Also notably, damage tolerance plays an important factor here: Most cracks are not per se catastrophic, and actually act as useful fatigue indicators (that need to be watched carefully!). Depending on crack position/length/propagation speed etc. different actions are prescribed.

Engineers have a variety of ways to detect metal fatigue in aircraft:

Visual inspection: sometimes cracks are visible to the naked eye, or can be seen under magnification
Auditory inspection: sometimes a thump sounding wrong can give a clue that there's an issue. It's not a primary means of checking for fatigue, but something that may clue in an astute engineer that something needs to be looked into
Ultrasound: Ultrasound uses very high pitched sound waves to image materials and can be used to find cracks inside materials
Radiology: xrays and other types of radio imaging can be used to find sub-surface cracks
Visible dyes: flourescent dyes in penetrating oils show up cracks which make it to the surface
Magnetic powders: these only work on iron-based parts which are rare on an aircraft but are used

Here's a good article that goes into some details on non-destructive fatigue testing.

In addition to that article Chapter 8 of the FAA Aviation maintenance Technician's Handbook (AMT) could well be titled "More than anyone ever wanted to know about inspecting for fatigue/damage"; the good stuff begins around page 8-18 (Nondestructive Inspection/Testing).

IMO, this is a much better answer than the accepted version.

Some metal fatigue can be spotted visually as an visible crack or as a collection of tiny cracks that can give the metal a 'frosty' look but most is done via non-visual non destructive testing techniques such as radiography (basically X-raying) or Ultrasonic testing to search for microfractures before they reach the problem stage. Visual checks are no use for platform critical damage as by the time you see it it is well into the failed zone which is why NDT techniques are used to detect an impending failure well before it causes a problem.
There are other techniques such as Dye Penetrant tests where a dye in a carrier fluid is painted into the surface and then wiped off. The fluid is light enough to penetrate and 'wick' into any fine cracks and will highlight cracks that are invisible to the eye. The dye is often fluorescent.
As for what can be done it very much depends in the extent and location of the cracking. Extensive damage and/or damage to critical area will be repaired by replacement, minor damage can be gouged out and welded up.
The best method of minimising fatigue it to prevent it and so most manufacturers will feed back fatiguing data from surveys to the design sections who will design out the weak point if one exists. Real life data trumps even the most extensive FEA predictions.

The pilot listens and notify the technicians that the plane is giving out strange noises.
And now seriously: For each plane type there are cards which parts need to be replaced or inspected after certain flight hours, start count or time. Together with required quality control at production and maintenance it should prevent metal fatigue incidents as much as possible.
And for the rest - @AndyW already mentioned techniques used during the inspections

Total take-off/landing cycles may be significant for some fatigue scenarios...https://en.wikipedia.org/wiki/Aloha_Airlines_Flight_243